The man, who did not want to be named, said he was in the car park of the Griffith Hotel on the night of July 15, 1977, at around 6.30pm, when Mr Mackay was shot.

The man claims a number of people were involved in the shooting, and after what made headlines around the country as Australia's first political assassination, he fled overseas, fearing for his own life.

He said he had not come forward for more than 30 years because he did not trust police.

Griffith police commander Superintendent Michael Rowan said investigations into Mr Mackay’s murder are continuing under Strike Force Fitr, which is comprised of detectives from the Homicide Squad and Griffith Local Area Command.

"Detectives were recently contacted by a man who claimed to have new information concerning Mr Mackay's death," Supt Rowan said.

"This information was followed up, however, it has not resulted in any significant development for investigators.

"Strike Force Fitr detectives continue to encourage anyone with information concerning Mr Mackay's death to contact Crime Stoppers. Information can be provided anonymously and will be treated in the strictest confidence," he said.

Mackay's son: Witness' claims "not true"

Donald Mackay's son Paul, a Griffith business man, said police had investigated the witness' claims already and he believed the story was "not true".

In the past he has said the family has always been hopeful but not confident their loved-one's remains would be found.

The whereabouts of the body of Liberal Party candidate Donald Mackay - and his murderer - still remain a mystery, but Melbourne man James Bazely was convicted of conspiring to the murder of the vocal campaigner against Italian Mafia group’s local marijuana trade in the Griffith region.

VIDEO: Watch the Crime Investigation Australia video on the murder of Don Mackay.

Peter Halloran, former Victorian Police homicide chief, said while there was no evidence of anybody except Mr Bazely being present at the killing, it was "possible" more people were involved.

In a Royal Commission six men – including mafia kingpin Bob Trimbole – were named, who may have ordered Mr Mackay’s assassination.

No one has ever been charged with the murder.

CRIME SCENE: Donald Mackay's minivan in the car park of the Griffith Hotel.

A $200,000 reward is available for information leading to the discovery of Mr Mackay’s body.

Police in bid to solve Mackay murder mystery

In 2012 Griffith police commander Superintendent Michael Rowan said he was “confident” a number of people still living in Griffith knew where Mr Mackay’s remains were dumped, urging them to come forward “anonymously if needed”.

“We are confident someone knows what happened to Mr Mackay’s body, and in what we believe may be a last-ditch effort to solve this matter, we are appealing for them to come forward,” Supt Rowan said.

“It has left a family forever wondering, and a community stained by events that occurred before many of its residents were born.

“In the decades since Mr Mackay’s disappearance, police have investigated many tip-offs about the location of his remains, to no avail.”

Last year police dug up a property in Hay in search of Mr Mackay's remains in what had been described as one of the biggest operations related to the case in the past 30 years.

UNSOLVED MYSTERY: Last year police dug up a property near Hay in a bid to solve the Mackay murder mystery.

What happened to Don Mackay?

Donald Mackay, aged 43 at the time, went missing from the car park of a hotel in Kooyoo Street, Griffith, on the evening of 15 July, 1977.

Blood and bullet cartridges were located near Mr Mackay’s locked van.

Police said extensive investigations and a 1984 coronial inquest concluded that Mr Mackay died of wilfully inflicted gunshot wounds.

It is believed he was murdered on the same day he disappeared.

Griffith police commander Superintendent Michael Rowan said the murder was a “travesty”.

“This is only compounded by the fact we don’t know what happened to his body,” Det Supt Rowan said.

In 2012 Minister for Police and Emergency Services, Michael Gallacher, said it was hoped the passage of time would encourage someone with information to come forward.

“Someone out there knows where Mr Mackay’s remains are, and that is information that would provide a grieving family some closure.

“This family has lived for 35 years not knowing what happened to their loved one. At the very least, they deserve to know his final resting place,” Minister Gallacher said.

Anyone with information that may assist police is urged to contact Griffith Local Area Command on 02 6969 4299 or Crime Stoppers on 1800 333 000.

1979 - The Woodward Royal Commission finds Mr Mackay was murdered by a Griffith-based cell of the Calabrian`Ndrangheta mafia. The commission names six people - including mafia kingpin Robert Trimbole - as influential members associated with the assassination of Mr Mackay.